1. Field of the Invention
The present invention relates, generally, to multi-disk devices. More specifically, the present invention relates to friction facings for multi-disk devices having improved lubrication characteristics.
2. Description of the Related Art
Multi-disk friction devices are employed in a wide range of applications as clutches or brakes. For example, such devices are frequently used in land-based vehicles. Generally speaking, such vehicles require three basic components: a power plant (such as an internal-combustion engine), a powertrain, and wheels. The powertrain""s main component is typically referred to as the xe2x80x9ctransmission.xe2x80x9d Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle.
Transmissions include one or more gear sets, each of which may include an inner sun-gear, intermediate planet gears supported by their carriers, and outer ring-gears. Various components of each gear set are held or powered to change the gear ratios in the transmission. The multi-disk pack-clutch is a friction device that is commonly employed as a holding mechanism in a transmission or differential. In addition, multi-disk friction devices also find use in industrial applications, such as wet brakes for braking the wheels on earth-moving equipment.
The multi-disk pack-clutch or brake-assembly includes a plurality of ring-shaped disks and has a clutch subassembly. The subassembly includes a set of plates arranged in a torsionally rigid manner and fixed against displacement on a disk carrier as well as a set of friction disks interleaved between one another and fixed against displacement on a hub. The clutch or brake assembly also typically includes a piston. When a component of a gear set is to be held, as during a particular gear range, a piston is actuated to cause the plates and friction disks to come in contact with one another. The plates mutually engage in a gearing manner, and the friction disks mutually engage in a gearing manner. The gear sets are mutually displaceable relative to each other in an axial direction and can be brought into and out of engagement in pairs. In xe2x80x9copen packxe2x80x9d operation, the plates and friction disks normally turn past one another without contact. In certain applications, it is known to employ several multi-disk friction devices in combination to establish different drive connections throughout the transmission or differential to provide various gear ratios in operation or to brake a component.
Multi-disk clutches or multi-disk brakes having disks that are interconnected, i.e., made in a single piece from frictional material, are also known in the related art. Examples of such devices are disclosed in DE 31 49 880 C2, DE 35 32 759 C1, and DE 31 18 565 A1.
Each friction disk includes a carrier plate made of, for instance, steel. The plate includes a friction surface on at least one annular face of the plate. The friction surface generally includes a fiber material manufactured from paper or a paper-like material. The structure of the plate surfaces is generally smooth. The confronting faces of the interleaved plates and friction disks are, therefore, covered with friction surfaces. WO 97/32678 discloses a special plate-surface structure made of steel and used to improve the coefficient of friction in the pairings of the friction disks and plates.
When a friction device is engaged, kinetic energy is converted into thermal energy and a considerable amount of heat is generated. If the friction surfaces get too hot, they can bum, which damages the friction surfaces and degrades the clutch""s or brake""s operational effectiveness, such as by wear and tear or lack of heat discharge. Additionally, the requirements placed on the service life of multi-disk clutches and similar units are exceptionally high. For example, during the service life of a clutch, the disks thereof are brought into and out of engagement with each other innumerable times, applying high axial forces and, thus, high surface pressures to each disk. Despite these requirements, the behavior of the power transmission is to remain unchanged, and each disk is to be provided a long service life. Failure of one or more disks leads to failure of the entire unit. And, the removal of defective disks and the installation of new ones are very laborious. Therefore, maintaining the behavior of the power transmission and providing a long service life for the disks are of utmost economic importance.
As a result, in the power-transmission units discussed above, lubrication of the individual components plays an important role. It must be ensured, in particular, that lubricating oil reaches the friction surfaces of the disks. For this purpose, lubricating oil is typically sprayed onto the friction surfaces. High temperatures are maintained, to the extent possible, within limits by the lubricating oil.
It is known in the related art to provide the friction surfaces with a porous, sponge-like structural arrangement, among others, such that a certain amount of oil storage is achieved. The stored oil is supplied to the friction surfaces when the clutch is applied.
Many causes of the failure of disks having such structural arrangement and others have already been examined. Such causes include improper lubrication, excessive frictional work or performance, and unfavorable properties of the friction lining.
Accordingly, there remains a need in the art for a power-transmission unitxe2x80x94in particular, a multi-disk friction device, such as a clutch or brakexe2x80x94the service life of which is increased as compared with known units and breakdowns of the disks of which are avoided. The present invention arranges the disks such that lubrication is optimized so that they transmit torque in an improved manner.
The present invention overcomes the disadvantages in the related art in an annular friction-clutch facing for a multi-disk clutch. The facing includes an inner edge and an outer edge defining a width of the facing. The facing further includes a first group of grooves formed on the facing and having a first cross-sectional area. Each groove of the first group has a first opening at the outer edge and a second opening at the inner edge remote from the first opening and is adapted to direct lubricating agents across the width over a substantial area of the facing. The facing further includes a second group of grooves formed on the facing and having a second cross-sectional area smaller than the first cross-sectional area. The second group of grooves includes first and second sets of grooves. The grooves of the first set are disposed in intersecting relationship with the grooves of the second set. The second group of grooves is adapted to remove excess of the lubricating agents on the facing.
Accordingly, one advantage of the present invention is that the friction facings are provided with grooves that ensure that the working face is provided with a residual supply of lubricating oil.
Another advantage of the present invention is that the grooves discharge the heat incurred during the xe2x80x9cclosed packxe2x80x9d operating mode of the friction device.
Still, another advantage of the present invention is that the grooves improve the friction properties of the multi-disk friction device.
Still, another advantage of the present invention is that relatively large streams of lubricating oil flow in the grooves, thereby substantially improving the way frictional heat is carried off within the clutch and, thus, contributing to the increased service life of the disks.
Still, another advantage of the present invention is that the grooves entirely wet the friction surfaces with lubricating oil by supplying remote areas of the disks with lubricating oil at all speeds occurring during operation of the disks.
Still, another advantage of the present invention is that the grooves counteract the formation of a film by the lubricating oil.
Still, another advantage of the present invention is that energy density is increased considerablyxe2x80x94the size of the disks can be reduced while maintaining the frictional work, or the frictional work can be increased by maintaining the size of the disks.
Still, another advantage of the present invention is that the streams of lubricating oil within the grooves do not obstruct the absorption of load upon engagement of the disks such that no time delay occurs.
Finally, these advantages are achieved in an annular friction-clutch facing for a multi-disk clutch that is operationally efficient and cost-effective to manufacture relative to such facings known in the related art.